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A S H RA E J O U RN A L a s h r a e . or g J A N U A R Y 2 0 1 44 6
BY YOUMING CH EN, MEMBER ASHRAE; HAITAO WANG; CARY W. H. CHAN; AND JIANYING QIN, MEMB ER ASHRAE
Detecting Faults In Hong Kong High-Rise
2013 ASHRAE TECHNOLOGY AWARD CASE STUDIES
HONORABLE MENTION
COMMERCIAL BUILDINGS, EXISTING
Maintaining nearly 1,200 VAV
terminals in a 36-story office
building is no easy feat. The
recipients of the Technology
Award Honorable Mention
developed a fault detection tool
that doesn’t require an extra
sensor and works with the
existing energy management
and control system.
ABOUT THE AUTHORS
Youming Chen is a professor of Hunan University in Changsha, Hunan, China. Haitao Wang is a project engineerof Hunan University in Changsha, Hunan, China. Cary W.H. Chan is a general manager at Technical Services andSustainability of Swire Properties Ltd in Hong Kong and Jianying Qin is an assistant building services manager of Swire
Properties Ltd in Hong Kong.
Cambridge House VAV Terminals
Location: Hong Kong
Owner: Swire Properties Ltd.
Principal Use: Office Building
Includes: Retail, restaurant and foyer
Employees/Occupants: 3,000
Gross Square Footage: 317,361
Conditioned Space Square Footage: 282,705
Substantial Completion/Occupancy: 2003
Occupancy: 100%
BUILDING AT A GLANCE
This article was published in ASHRAE Journal, January 2014. Copyright 2014 ASHRAE. Posted at www.ashrae.org. This article may not be copied and/or distributed electronically or in paper form withoutpermission of ASHRAE. For more information about ASHRAE Journal, visit www.ashrae.org.
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J A N U A R Y 2 0 1 4 a s h r a e . or g A S H RA E J O U RN A L 4 7
Each floor in the building is served by a single duct
VAV air-conditioning system. Constant air volume boxes
provide 1,377 cfm (650 L/s) of fresh air for each floor.
Fresh air is delivered to the air-handling unit (AHU)
room of each floor by three fresh air fans. Return air is
sent to the AHU room through a ceiling void.
The layout of an air-conditioning system for a typicalfloor is shown in Figure 1. An AHU with monitoring and
control instrumentation provides an adequate fresh
airflow rate, suitable supply air temperature, and supply
air pressure. VAV terminals are used to maintain zone
air temperature at the desired value through regulating
supply air volume into the zones.
VAV terminals are likely to fail after running for several
years. VAV terminal faults cause zone air temperatures
out of the desired values, poor thermal comfort and
more energy consumption.
The 1,186 VAV terminals are dispersed in the closed ceil-
ing void. It is difficult to check all VAV terminals manu-
ally because of the labor involved and issues with access
to tenant spaces. An investigation of VAV terminals for a
similar office building took two technicians almost six
months to complete. Current energy management and
control systems (EMCS) do not diagnose faults of VAV
terminals. But, the effective use of a fault detection and
diagnosis (FDD) tool for VAV terminals can help improve
thermal comfort, increase equipment service life, and
reduce maintenance costs and energy consumption.
For the Cambridge House project, an online FDDtool was developed to find and identify VAV terminal
faults. The FDD tool can analyze the operating data in
an EMCS automatically and provide building operators
with user-friendly fault information of VAV terminals.
The implementation of the FDD tool in Cambridge
House covers two phases: tool development (January
2009 to December 2009) and application trial (January
2010 to present). In the application phase, many VAV
terminal faults were verified and corrected because of
fault reports provided by the tool.
FDD Tool for VAV Terminals The FDD tool for VAV terminals adopts a robust fault
detection and diagnosis strategy. In the strategy, a
residual-based cumulative sum (CUSUM) control chart
is used to detect faults. And, some expert rules derived
from mass and energy balances are designed to find
fault sources in VAV terminals. The FDD tool is installed
in a stand-alone computer. A schematic of the FDD tool
integrated with the EMCS is shown in Figure 2.
The FDD tool has no special operational requirementsfor air-conditioning systems, and doesn’t need an addi-
tional sensor. It relies only on sensor data and control
signals available in a typical EMCS.
The tool has five functions: operating data acquisition,
fault detection, fault diagnosis, automatic generation of
VAV box trend log, and automatic fault report. Figure 3
shows the interface of the FDD tool. On the left is a lay-
out of VAV terminals according to their location in the
building.
The icon color of VAV terminals is changed in real time
according to the terminals’ operating status. Green
means normal; red means faulty; magenta means erro-
neous data communication for the terminal; yellow
means a special requirement for the terminal; white
means unused or no data.
The center of the interface shows detailed informa-
tion for a selected terminal. On the right is an array of
floor-switching buttons. Clicking other buttons gener-
ates reports such as a fault report for the day and a fault
report for fault verification and repair. Trend logs of ter-
minals can help operators assess the original design of
LEFT Cambridge House in Hong Kong saved 13% on its electrical bill by installing afault detection tool to help building operators identify faults and make repairs beforethey could waste energy.
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A S H RA E J O U RN A L a s h r a e . or g J A N U A R Y 2 0 1 44 8
2013 ASHRAE TECH NOLOGY AWARD CASE STUDIES
VAV terminals and further look into fault sources in VAV
terminals. Operators can set a tenant special require-
ment for a VAV terminal. The FDD tool can be easily
extended to any other VAV air-conditioning system by
VAV Terminals and AHUs
LAN
DDC
SQL Server
The FDD Tool The EMCS CentralControl Station
Request ing Data from SQL Sending Data Per 5 Minutes
FIGURE 2 Online implemention of the FDD tool in EMCS.
FIGURE 1 Layout of air-conditioning system for a typical floor.customizing the interface according to the number and
location of VAV terminals.
Innovation The online FDD tool is probably one of the first EMCS
tools to diagnose the VAV terminal faults in a commer-
cial building. Extensive tests have been conducted on
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A S H RA E J O U RN A L a s h r a e . or g J A N U A R Y 2 0 1 45 0
2013 ASHRAE TECH NOLOGY AWARD CASE STUDIES
site to verify the performance of the tool. The
main innovations include:
A site survey study on the faults of VAV termi-
nals was conducted in Cambridge House and 13
main faults were identified. The fault diagnosis
tool was developed to address these faults. A residual-based CUSUM control chart is used
to detect faults. It improves the accuracy of fault
diagnosis through removing adverse effects of
serial correlation in data, but also enhances the
robustness of fault diagnosis through reducing
the impacts of normal transient changes.
Some expert rules, derived from mass and
energy balances, are used to find the fault sources
in VAV terminals. These rules are easy to understand,
which can help to convince operators to use the FDD tool.
The tool shows the operating condition of VAV termi-
nals and the source of the fault. The tool uses the rated
parameters of terminals as well as the sensor and con-
trol signals that are commonly available in an EMCS.
The FDD tool can provide fault statistics and generate
a fault report for verification. Faults of VAV terminals are
separated into different grades according to the severity
of faults. The fault list can facilitate fault rectification and
improve the efficiency of maintenance and management.
Special tenant requirements are considered in the tool
to reduce false alarms. Special requirements include
vacation, interior design work, renovation projects, etc.
FIGURE 3 Interface of the FDD tool.
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J A N U A R Y 2 0 1 4 a s h r a e . or g A S H RA E J O U RN A L 5 1
Operation and Maintenance The tool checks and analyzes the operating data in the
EMCS automatically, and provides building operators with
clear fault information of VAV terminals, which improve
the quality of VAV operation and maintenance. Operators
can work quickly with the FDD tool, as its operation issimple. The FDD tool checks the operating status (on/off)
of VAV terminals and AHUs automatically. The operating
status has no effect on the operation of the tool, which can
operate continuously without any maintenance or cost.
Energy Benefits The implementation of the FDD tool has significantly
improved the energy efficiency of Cambridge House.
The monthly cooling load for weekdays in 2009 and 2010
(8 a.m. to 6 p.m., Monday through Friday, and 8 a.m. to
2 p.m. on Saturday, excluding the rest of the weekends
and public holidays) are listed in Table 1. The total cool-
ing load of Cambridge House was 6,430,883 kWh in
2010, a decrease of 980,250 kWh from the previous year.
The total annual electricity of air-conditioning systems
decreased by 13.23% after applying the FDD tool.
Conclusion The FDD tool has provided an effective approach to
detect and diagnose VAV terminal faults, which improved
thermal comfort, service quality, and reduced mainte-
nance costs and labor. Annual electric savings is 13.23%.
Table 1 Monthly cooling load of Cambridge House for weekdays in 2009 and2010 (based on the data from EMCS).
MONTH 2009 COOLI NG LOAD (KWH) 2010 COOLING LOAD (KWH)
January 307,454 254,106
February 455,624 267,892
March 431,875 399,369April 450,375 370,491
May 657,499 594,552
June 883,080 649,638
July 946,323 823,336
August 950,534 845,983
September 911,237 825,909
October 665,992 599,282
November 454,377 460,675
December 296,763 339,652
TOTAL 7,411,133 6,430,885
SAVING 13.23%
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